This invention relates to an improvement in a contacting type surface temperature sensor adapted to be brought into contact with a surface of a solid to measure the temperature thereof, and more particularly, to a surface temperature sensor which is capable of minimizing a measurement error even when the posture of the sensor with respect to the surface, the temperature of which is to be measured, of a solid varies to a diagonal state, i.e., even when the angle between an object surface of the solid and the sensor contacting the same surface varies to an angle smaller than 90.degree., and which has a superior durability.
A contacting type surface temperature sensor utilizing a thermocouple has a thin-belt-like resilient contact member. When this contact member consists of a spring type thermocouple plate, or a thin plate spring with a thermoelement, such as a thermocouple or a thermistor, supported on the central portion thereof, the contact member is fixed at its both ends to the free end portion of a support member so that the contact member projects semicircularly in side elevation, to thereby form a temperature measuring portion of the sensor.
When this surface temperature sensor is used, the intermediate portion of the semicircular contact member is brought into contact with the surface of a solid the temperature of which is to be measured, and then pressed lightly against the surface to slightly flatten the semicircular portion of the contact member, whereby a part (contact surface) of the contact member is engaged closely with the object surface of the solid. This contact member is formed so as to enable itself to reliably contact an object surface, the quantity of the heat, which is transferred between the contact member and an object surface when the contact member is engaged with the object surface to be minimized, and the temperature drop at the object surface at such a time to be thereby minimized. The construction of this surface temperature sensor is determined with consideration given to, especially, a solid having a small thermal capacity.
A method of making the contact member extremely thin so as to reduce the thermal capacity thereof is employed as means for enabling the contact member to be pressed against the object surface so that the contact member can thermally sufficiently contact the object surface and the occurrence of transfer of heat between the contact member and object surface can be minimized. However, when the thickness of the contact member is reduced to such an extent, the pressing force thereof to be applied to an object surface decreases, so that the contact member is not fitted accurately along the object surface.
In order that the contact member can reliably contact the object surface of a solid, the thickness of the contact member is increased to increase the pressing force thereof. However, if the thickness of the contact member is increased, the thermal capacity thereof increases. Therefore, when the generation of heat is to be measured in an object solid having a small thermal capacity and a low pressure resistance, for example, a semiconductor device, such a contact member is not suitably used. A surface temperature sensor in which a contact member is supported on a metallic auxiliary spring with a view to eliminating these problems is proposed as disclosed in, for example, Japanese patent publication No. 46-25795.
This surface temperature sensor "is provided with a thermocouple element joined to a thin-belt-like resilient thermocouple or a thin thermocouple wire so as to extend to a predetermined shape, and a metallic auxiliary spring means for the thermocouple element, and formed so that, when the temperature of an object surface is measured, the thermocouple element contacting this surface is supported on the metallic spring means in the same temperature region of the thermocouple element and spring means".
The temperature sensor of the above-described construction consists of a thermoelement composed of a thermocouple, and a spring means supporting the thermoelement, and the temperature measuring portion of the sensor has a complicated construction and a comparatively large thermal capacity.
The thermocouple and the spring means supporting it are fixed to a support member. It is necessary that a heat-sensitive portion of the thermoelement be in press-contact with an object surface accurately (closely) in all temperature measuring operations. Therefore, the heat-sensitive portion requires to be engaged with an object surface quietly. This causes the use of the sensor to be restricted. Namely, it is difficult to momentarily measure the temperature of, for example, a moving solid with which the heat-sensitive portion of the sensor cannot be easily engaged.
If the end portions of a contact member are fixed to a support member of the temperature sensor, fatigue of metal occurs at the fixed end portions of the contact member, so that the contact member is bent or broken. Therefore, it can be said that such a temperature sensor has a problem with respect to the mechanical strength as well.
The end portions of the contact member, which are fixed to the support member or the body of the temperature sensor, cause further problems. Namely, since the root portions of the contact member are fixed, the contact member is necessarily deformed to the shape of a cantilever. This causes the degree of freedom of deformation of the spring to decrease, and the contact surface of the contact member cannot accurately and easily engage the surface of an object solid.
Consequently, for example, when the temperature sensor is brought into contact with an object solid in motion to momentarily measure the temperature of the surface thereof, they do not engage with each other excellently, and an error would occur in a detected temperature.
In more detail, when the contact member engages the surface of an object solid, the deformation of the contact surface of the contact member does not progress, for example, from a semicircular shape to an elongated arcuate shape, i.e., the width or area of the contact surface does not gradually increase but, when the deformation of the contact member has progressed to a certain extent, a part of the contact surface thereof floats from the object solid, so that that part of the contact member on which a temperature measuring element which is important for the measurement of the temperature of an object surface is provided, or a hot junction does not accurately contact the object solid.
These problems will be described with reference to illustrations. As shown in FIG. 10(a), both ends 1a and 1b of a contact member 1, which consists of a thin plate of a thermocouple with a hot junction c (or a heat-sensitive portion) provided on the central section of the thin plate, or a thin plate with a heat-sensitive element, such as a thermistor provided on the central portion thereof, or a thin wire type thermocouple, are fixed to a body 2 (or a support member) of a temperature sensor so that the contact member 1 is bent generally to a semicircular shape. The measuring of the temperature of an object solid 3 with this contact member 1 engaged therewith will now be described.
When the central portion of the semicircular contact member 1 fixed at its both ends to the sensor body 2 as shown in FIG. 10(a) is engaged lightly with the object solid 3, the hot junction c and the center of a contact surface 4 shown in FIG. 10(b) agree with each other.
A segment Q on the contact surface 4 represents a stress-concentrated portion occurring when the contact member 1 engages the object solid 3. This means that, when the contact member 1 is deformed slightly, the hot junction c exists on the contact surface 4 with the contact surface area at an insufficiently low level, and that, therefore, an accurate temperature measuring operation cannot be carried out.
When the sensor body 2 is then moved toward the object solid 3 in the direction of an arrow D shown in FIG. 11(a), the width of the contact surface 4 gradually increases as shown in FIG. 11(b). In this stage, the hot junction c is still positioned on the central portion of the contact surface 4, and the contact surface area is sufficiently large, so that the temperature of the object solid can be accurately measured.
The variation (increase) of the area of the contact surface 4 will now be discussed. When the contact member 1 is pressed toward the surface of the object solid 3 in the direction of the arrow D to be engaged therewith, a force shown by an arrow E and directed from the fixed support point 1b to a stress-concentrated portion Qb on the object solid 3 occurs. The force shown by this arrow E is divided into components working in two directions, i.e. a component of the arrow D by which the contact member 1 is pressed toward the object solid 3, and a component of an arrow F by which the contact member 1 is compressed toward the central portion thereof.
A question as to whether the component working in the direction of the arrow F serves to reliably engage the contact member 1 with the surface of the object solid 3 will now be discussed. When the sensor body 2 is brought closer to the object solid 3 so as to deform the contact member 1 as shown in FIG. 12(a), the component of the arrow F works toward the central portion of the contact member 1, so that the central portion floats from the object solid 3 to cause the hot junction c to be separated by a distance .delta. from the surface of the object solid 3. The details of such a movement of the central portion designated by a circle R in FIG. 12(a) are shown in an enlarged front elevation of the same portion in FIG. 12(c).
When the contact member is in this condition, the contact surface 4 is separated into contact surface portions 4a and 4b as shown in FIG. 12(b). The above-mentioned upward removal of the hot junction c from the surface of the object solid 3 causes an error of a detected temperature, and it is necessary that this phenomenon be prevented.
If the contact member 1 is engaged momentarily with the surface of the object solid 3 as shown in FIG. 12(a), the hot junction c is not heated directly by the object solid 3. Therefore, it is clear that an error of a detected temperature becomes large.
The above is a description of the case where the contact member 1 is engaged in a regular posture (in which the sensor body 2 is applied to the surface of the object solid 3 so that the direction in which a pressing force is applied to the sensor body is at right angles to the surface of the object solid 3) with the surface of the object solid 3. When the sensor body 2 is applied to the surface of the object solid 3 so that the direction of a pressing force applied to the latter is diagonal with respect to the latter, some more problems arise.
FIGS. 13(a), 13(b), 14(a), 14(b), 15(a) and 15(b) illustrate this case. FIGS. 13(a) and 13(b) correspond to FIGS. 11(a) and 11(b), and indicate that the hot junction c (or heat-sensitive portion) is positioned in the central portion of the contact surface 4, and that an error of a detected temperature does not substantially occur.
When the object solid 3 inclines with respect to the body 2 of the temperature sensor, or when the sensor body 2 is engaged incliningly with the object solid 3, as shown in FIG. 14(a), the heat-sensitive portion c gradually leaves a center line S. As a result, the hot junction c moves toward a corner portion of the contact surface 4 as shown in FIG. 14(b). In this case, the hot junction c is about to leave the contact surface 4, and deviation occurs between a temperature-measuring center c' and the hot junction c.
FIGS. 14(a) and 14(b) show an example of the posture of the contact member 1, which often occurs while the temperature of, for example, a moving object is measured with a contacting type temperature sensor. In this case, the temperature-measuring center c' deviates from the hot junction c, so that a temperature lower than an actual temperature is detected. Namely, an error occurs in a temperature measuring operation in this case.
FIGS. 15(a) and 15(b) show the condition of the sensor body 2 extremely inclined with respect to the object solid 3 with the hot junction c removed or about to be removed from the contact surface 4. In this condition, the accurate transmission of the heat of the object solid to the hot junction c can hardly be expected, so that a considerable error occurs in a detected temperature.
When the sensor body 2 inclines extremely with respect to the object solid 3 as shown in FIG. 15(a), one side portion of the contact member 1 is bent as shown by 1m with a comparatively large radius of curvature, while the other side portion thereof is bent as shown by 1n with a small radius of curvature. When the contact member 1 is bent with a small radius of curvature 1n in this manner, the fixed portion 1b is bent extremely, and large stress occurs therein, so that permanent deformation occurs in the contact member 1. This causes an error in a detected temperature to increase, and the contact member 1 to be finally broken. Moreover, since the hot junction c is moved to an end portion of the contact surface 4, it becomes difficult to measure the temperature of the object surface accurately.